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<h1><a href="https://archiveofourown.org/works/29693214">The Kasen Extermination Expedition</a> by <a class='authorlink' href='https://archiveofourown.org/users/bagoum/pseuds/communistkasen'>communistkasen (bagoum)</a></h1>

<table class="full">

<tr><td><b>Category:</b></td><td>Touhou Project</td></tr>

<tr><td><b>Language:</b></td><td>English</td></tr>

<tr><td><b>Status:</b></td><td>Completed</td></tr>

<tr><td><b>Published:</b></td><td>2021-02-25</td></tr>

<tr><td><b>Updated:</b></td><td>2021-02-25</td></tr>

<tr><td><b>Packaged:</b></td><td>2021-05-16 02:29:03</td></tr>

<tr><td><b>Rating:</b></td><td>General Audiences</td></tr>

<tr><td><b>Warnings:</b></td><td>No Archive Warnings Apply</td></tr>

<tr><td><b>Chapters:</b></td><td>1</td></tr>

<tr><td><b>Words:</b></td><td>1,930</td></tr>

<tr><td><b>Publisher:</b></td><td>archiveofourown.org</td></tr>

<tr><td><b>Story URL:</b></td><td>https://archiveofourown.org/works/29693214</td></tr>

<tr><td><b>Author URL:</b></td><td>https://archiveofourown.org/users/bagoum/pseuds/communistkasen</td></tr>

<tr><td><b>Summary:</b></td><td><div class="userstuff">
              <p>A married couple debates the best way to educate their growing child.</p>
            </div></td></tr>

<tr><td><b>Relationships:</b></td><td>Ibaraki Kasen/Yakumo Yukari</td></tr>

<tr><td><b>Comments:</b></td><td>1</td></tr>

<tr><td><b>Kudos:</b></td><td>9</td></tr>

</table>

<a name="section0001"><h2>The Kasen Extermination Expedition</h2></a>
<div class="story"><div class="fff_chapter_notes fff_head_notes"><b>Author's Note:</b><blockquote class="userstuff">
      <p>Direct sequel to https://archiveofourown.org/works/29667504</p>
    </blockquote></div><div class="userstuff module">
    
    <p>"Good morning, Reimu. Keeping the shrine clean, I see." Kasen stepped out from behind a pillar, smiling, and waved at me. I've never seen her approach the shrine, but somehow she would always appear from behind that pillar. Well, I don't need to find out how she does it. Because today--</p>
<p>"Ha! I've been waiting for you!" I dropped my broom and quickly rushed back into the shrine to collect my gohei and needles. When I emerged I stood on the edge of the shrine's platform, as to gain a few feet of height over her, and announced, in my most threatening voice, "It's time for your extermination!"</p>
<p>But in response to my declaration of war, she only laughed. "Don't bother, Reimu. You can't exterminate me."</p>
<p>I puffed out my chest to look as imposing as possible. "I can even exterminate Yukari, so why would I have a problem dealing with you?"</p>
<p>"Because--" she paused and shrugged slowly for emphasis-- "I'm human. And all your weapons are anti-youkai weapons. Instead of throwing needles at me, you'd be better off throwing dry beans. I prefer rajma, by the way."</p>
<p>"That's not true. These weapons work against everything! Like during the Scarlet Mist incident--"</p>
<p>"Vampires are youkai."</p>
<p>"But Sakuya--"</p>
<p>"Let you win, since she herself couldn't directly go against Remilia's wishes. Do you actually think you can beat her?"</p>
<p>"Then, Kaguya and--"</p>
<p>"Lunarians are more or less human, but the Hourai Elixir is not."</p>
<p>"Aha! But Sanae is human and--"</p>
<p>"She's in the same boat as you, but weaker."</p>
<p>"Dammit... then what about Kanako? She's neither human nor youkai."</p>
<p>Kasen frowned momentarily. "Correction. Your powers are oriented around fighting youkai, gods, and ghosts. Essentially, the nonhuman. That includes Yuyuko and the half-ghost samurai lawnmower, who have been so regrettably forgotten."</p>
<p>No, no, there had to be something... "Ah, then consider Tenshi--"</p>
<p>"Celestials are more or less youkai."</p>
<p>"What about--"</p>
<p>"Oni are effectively youkai."</p>
<p>"Dammit... That only leaves... Byakuren, I guess. Yeah, how about that? Byakuren is my proof that my weapons can beat humans!"</p>
<p>Kasen keeled over as if she had been attacked by a sudden stomachache, but before I could ask her what had happened, she threw her head back and broke into a roaring laughter. "Byakuren?! BYAKUREN?!!!??! That vampire is STILL going around pretending to be human?!!?!?! AhahaHAHA!!!! If nothing else, you have to applaud her god damn PERSISTENCE!!!!"</p>
<p>I couldn't help but feel like Kasen had momentarily been taken over by the spirit of a crazed elephant. Worried, I tried to respond non-provocatively. "Aren't you using a few too many exclamation marks? Byakuren is human, there's nothing odd about it."</p>
<p>Only after her outbreak had calmed was she able to return to her normal standing posture. "I guess it's not well known around here. Then, how about this?" She jumped up onto the shrine's platform and stood facing me, then grasped my shoulders in her hands and craned her head over to my left ear... I really wish it were Marisa doing this rather than my philosophy teacher. Whispering into my ear... <i>Reimu no koto ga suki da★ze...</i> Yes, just like that. I love you too, Marisa...</p>
<p>"Cut deep into her flesh, and look closely at her blood. And then, only if you yet desire it, I shall reveal to you the truth."</p>
<p>Her uncharacteristically inauspicious words sent a chill down my spine and rung frigidly in my ears, but when she stepped back she was still wearing her simple and pure smile. "Anyways, for now, take my word that Byakuren does not count as <i>human</i> in any calculation. And thus, you are weak against humans. But you should have already been able to guess that. Didn't you yourself tell Yorihime that you were at a disadvantage because your fighting style was explicitly anti-youkai?"</p>
<p>"H-how do you know that?!"</p>
<p>"I... talked to the people who were with you at that time?" The tone of her response indicated that this was an obvious conclusion I should have come to. Well, I guess if she hadn't prefixed it by telling me to <i>literally</i> cut someone, I would probably have come to that conclusion.</p>
<p>"What's this, Kasen? I see you're getting quite close with Reimu here."</p>
<p>I turned around and saw Yukari standing a few feet away, also on the shrine's platform, with a stack of papers in one hand. Her face was contorted with discontentment, but... it was a bit strange somehow. I guess... it looked less like her characteristic godlike fury and more like petty human jealousy. But in context, that makes no sense, so I must just be seeing things wrong here in the overhang's shade.</p>
<p>Kasen laughed, and I could tell by her sheepish tone that she was guilty of whatever Yukari was accusing her of. "Instrumentally. There are some things which can't be said out loud. Don't worry, I try not to do it often to others."</p>
<p>A voiceless sigh escaped Yukari's mouth as she turned her gaze to me. "Reimu, this is a report that was compiled regarding the last incident. You're growing up now, so you need to start reading these. Kasen, do make sure she reads this. Give her a quiz or something."</p>
<p>Kasen clicked her tongue, slowly, three times. "No, no. For these kinds of things you need positive reinforcement based on effort rather than performance."</p>
<p>Both Yukari and I looked quizzically at her, but I was the first to speak. "What does that mean?"</p>
<p>Kasen put her finger to her chin. "Hmm... I guess..." Then, her eyes lit up and a smile broke across her face. "Aha! How about this? Reimu, if you read this and do your best to explain to me what you learned, I'll cook for you. Since the food you eat normally is utter garbage."</p>
<p>Yukari interjected. "But how long are you going to do that for? She needs to get in the habit of reading these, as part of her duty as the Hakurei shrine maiden. Are you going to waltz over and make dinner for her every time I hand her a report?"</p>
<p>"Of course not. I'll gradually pull back on the rate of reward and also introduce variability into the frequency, which is known to maintain high response rates. Once she becomes proficient in this task, the reinforcement arising from the consequences of this task, namely her increased ability to deal with incidents as a result of her improved knowledge, will take over as the primary reinforcer. And at that point I'll be able to pull my reinforcer for a more apt usage."</p>
<p>I looked back at Yukari, who was just as confused as me. She spoke with an uncharacteristic degree of uncertainty. "Well, I suppose I haven't read through that stack of books yet. I'll let you handle it for now."</p>
<p>Kasen smiled, content with her little show. "So she says, Reimu. You have homework now." It's kind of impressive how she can run circles around even Yukari in an argument. But I think I'd prefer the quiz to whatever Kasen is planning. That said... Kasen's handcooked dinner does sound nice. Maybe I should read this report after all.</p>
<p>"Wait, wait, wait." I nearly forgot the most important thing! I turned to Yukari and pointed my gohei at her. "I'll give up on Kasen, but I still need to exterminate you!"</p>
<p>Yukari suddenly came to life, her wicked smile streaking across her visage and her cruel gaze focusing in on my defiant frown. She swung her arms out wide, as if to challenge me, though she yet held the report tightly in her right hand. A light breeze blew, lifting the hair she had let down so it floated just enough to give off the impression of a fluffy golden cloud. "Oh? Which one of my myriad plots have you uncovered this time, child of man? With which proof shall you challenge my eternal reign?"</p>
<p>Why is she so happy about this...? No, that's not important. What's important is that I have to exterminate her! "Last time, you, uh, threatened Kasen into working with you! That's illegal! It's... duress!" As soon as I said this last word I heard Kasen snickering behind me, but I couldn't turn around to see what was so funny.</p>
<p>Yukari frowned. "I hypothetically could have threatened her, but do you actually have any evidence that I did?"</p>
<p>"I said it before and I'll say it again! <span class="blue">It's impossible for humans and youkai to cooperate, so you must have threatened her!</span>"</p>
<p>With her free hand, Yukari pointed at the needles I was holding. "Who made those needles?"</p>
<p>"I... I wouldn't know th--"</p>
<p>"Who made those needles?" Her calm voice struck me with the force of a tornado, and, overpowered by its authority, my voice was rendered impotent and I could only mouth a response. Yukari, with a smirk, uttered the words I could not. "<span class="red">Kogasa, a youkai, made those needles for Reimu, a human, of her own free decision. Proof by example. It is possible for humans and youkai to cooperate.</span>"</p>
<p>Damn...! She was right... my entire extermination plot was misguided from the start...! Should I give up and admit that I was wrong? Or should I make up a stupid and definitely bullshit excuse to try to prolong my defeat for a few seconds? Hmm... The choice is obvious!</p>
<p>"Fine! Then I'll use my trump card! <span class="blue">As the Hakurei shrine maiden, I have the right to exterminate youkai at will, regardless of crime supposed or actual!</span> I don't need a reason to exterminate you!"</p>
<p>Yukari's hair fell back down, the dynamism in her face quickly flattened, and her voice lacked energy when she responded. "That's no good, Reimu. I can't let you exterminate me, or the other youkai, unless you have a good reason. <span class="red">I do not recognize any such right, and therefore it does not exist.</span>" She locked her gaze with mine and suddenly began striding towards me. At this distance?! Is she trying to run me over?! I stepped back, but-- Kasen is that way! I'll run into her instead if I keep going! In that case... The best way to dodge a spear is... perpendicular, yes, perpendicular! But which way is perpendicular? The sky is perpendicular to the ground, right?-- before I could devise another plan of escape, Yukari's hand reached out towards my face, quickly filling up my field of vision until I could see nothing but the white of her glove. </p>
<p>No no stop don't come any closer! I squeezed my eyes shut and shouted with all my forces "No! I don't want to go to Makai!" as if my entreaty would have a chance of stopping the demon closing in on me.</p>
<p>The sensation of her cold fingers crushing my skull as if it were a tomato... never came. I slowly opened one eye, and saw that Yukari had disappeared, and that the stack of papers she had been holding was now being squeezed by my own hands. I looked at it, unsure what to make of this situation, but I was too dazed to make out the words on the cover.</p>
<p>From behind, Kasen softly placed a hand on my shoulder. "If you read that report, you should be able to find a few things to exterminate Yukari over. She's looking forward to it, so do it well for her sake too, alright?"</p>
<p>I turned around and, in response to Kasen's kind smile, could only nod meekly. The extermination will have to wait for another time. At least until after dinner.</p>
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